SOIL DAMPING FORMULATION IN NONLINEAR TIME DOMAIN SITE RESPONSE ANALYSIS

Nonlinear time domain site response analysis is used to capture the soil hysteretic response and nonlinearity due to medium and large ground motions. Soil damping is captured primarily through the hysteretic energy dissipating response. Viscous damp-ing, using the Rayleigh damping formulation, is often added to represent damping at very small strains where many soil models are primarily linear. The Rayleigh damping formulation results in frequency dependent damping, in contrast to experiments that show that the damping of soil is mostly frequency independent. Artificially high damp-ing is introduced outside a limited frequency range that filters high frequency ground motion. The extended Rayleigh damping formulation is introduced to reduce the over-damping at high frequencies. The formulation reduces the filtering of high frequency motion content when examining the motion Fourier spectrum. With appropriate choice of frequency range, both formulations provide a similar response when represented by the 5% damped elastic response spectrum.

The proposed formulations used in non-linear site response analysis show that the equivalent linear frequency domain solution commonly used to approximate non-linear site response underestimates surface ground motion within a period range relevant to engineering applications. A new guideline is provided for the use of the proposed formulations in non-linear site response analysis.     

INTEGRATED PASSIVE-ACTIVE SYSTEM FOR SEISMIC PROTECTION OF A CABLE-STAYED BRIDGE

This paper presents an integrated passive-active (i.e. hybrid) system for seismic response control of a cable-stayed bridge. Since multiple control devices are operating, a hybrid control system could alleviate some of the restrictions and limitations that exist when each system is acting alone. Lead rubber bearings are used as passive control devices to reduce the earthquake-induced forces in the bridge and hydraulic actuators are used as active control devices to further reduce the bridge responses, especially deck displacements. In the proposed hybrid control system, a linear quadratic Gaussian control algorithm is adopted as a primary controller. In addition, a secondary bang-bang type (i.e. on-off type) controller according to the responses of lead rubber bearings is considered to increase the controller robustness. Numerical simulation results show that control performances of the integrated passive-active control system are superior to those of the passive control system and are slightly better than those of the fully active control system. Furthermore, it is verified that the hybrid control system with a bang-bang type controller is more robust for stiffness perturbation than the active controller with a μ-synthesis method, and there are no signs of instability in the over-all system whereas the active control system with linear quadratic Gaussian algorithm shows instabilities in the perturbed system. Therefore, the proposed hybrid protective system could effectively be used for seismically excited cable-stayed bridges.     

The geochemical evolution of very dilute CO2‐rich water in Chungcheong Province,Korea: processes and pathways

A geochemical study was carried out on the CO₂‐rich water occurring in granite areas of Chungcheong Province, Korea. In this area, very dilute and acidic CO₂‐rich waters [62–242 mg l^?1 in total dissolved solid (TDS), 4.0–5.3 in pH; group I) occur together with normal CO₂‐rich waters (317–988 mg l^?1 in TDS, 5.5–6.0 in pH; group II). The concentration levels and ages of group I water are similar to those of recently recharged and low‐mineralized groundwater (group III). Calculation of reaction pathways suggests that group I waters are produced by direct influx of CO₂ gas into group III type waters. When the groundwater is injected with CO₂, it develops the capacity to accept dissolved solids and it can evolve into water with very high solute concentrations. Whether the water is open or closed to the CO₂ gases becomes less important in controlling the reaction pathway of the CO₂‐rich groundwater when the initial pco ₂ is high. Our data show that most of the solutes are dissolved in the CO₂‐rich groundwater at pH > 5 where the weathering rates of silicates are very slow or independent of pH. Thus, groundwater age is likely more important in developing high solute concentrations in the CO₂‐rich groundwaters than accelerated weathering kinetics because of acidic pH caused by high pco ₂.     

EVALUATION OF CAPACITY SPECTRUM METHOD FOR ESTIMATING THE PEAK INELASTIC RESPONSES

The accuracy of the capacity spectrum method (CSM) depends on the precise estimation of equivalent period and damping ratio as well as the modification of the demand spectrum. In this paper, the CSM provided in ATC-40 for estimating the peak inelastic responses is evaluated. First, the effect of equivalent period and damping ratio estimation on the accuracy of the CSM is assessed. Analyses results indicate that the difference between estimation methods is large when the structural nonlinearity is large, but becomes negligible as the hardening ratio increases. Next, the reduction factors provided in ATC-40 and Eurocode are evaluated. It is found that the acceleration responses obtained using the factor of Eurocode is closer to the actual ones than those obtained using the factors of ATC-40. Finally, the demand spectrum is constructed using the peak absolute acceleration and pseudo-acceleration. The results obtained using the peak absolute acceleration is found to be generally larger than those obtained using the pseudo-ones. Since the original CSM generally underestimates the response, the use of peak absolute acceleration in the construction of demand spectrum produces the response relatively closer to the exact one. However, the use of peak absolute acceleration overestimates the response more when the original CSM overestimates the response.     

“韩流”对韩国旅游形象的影响

本文在广泛调查的基础上,运用多元统计技术分析了“韩流”对韩国旅游形象的影响程度,并探讨了访问意向与实际到访、游后评价以及旅游形象之间的关系等重要问题。     

A SUMMARY OF RESULTS OF SIMULATED SEISMIC LOAD TESTS ON REINFORCED CONCRETE BEAM-COLUMN JOINTS,BEAMS AND COLUMNS WITH SUBSTANDARD REINFORCING DETAILS

The results of some simulated seismic load tests on reinforced concrete one-way interior and exterior beam-column joints with substandard reinforcing details typical of buildings constructed in New Zealand before the 1970s are described. The tests were conducted using both deformed and plain round longitudinal reinforcement. The interior beam-column joint cores lacked transverse reinforcement and the longitudinal bars passing through the joint core were poorly anchored. The exterior beam-column joint units contained very little transverse reinforcement in the members and in the joint core. In one exterior beam-column joint unit the beam bar hooks were not bent into the joint core. That is, the hooks at the ends of the top bars were bent up and the hooks at the ends of the bottom bars were bent down. This anchorage detail was common in many older buildings constructed before the 1970s. In the other exterior beam-column joint unit the hooks at the ends of the bars were bent into the joint core as in current practice. The improvement in performance of the joint with beam bars anchored according to current practice is demonstrated. In addition, tests were conducted on interior joints with lap splices in the beam longitudinal reinforcement bars near the column face. The tests were conducted using both deformed and plain round longitudinal reinforcement. Tests were also conducted on columns with plain round bar longitudinal reinforcement and inadequate transverse reinforcement.

The reinforcing details were close to identical to those in an existing seven storey reinforced concrete building that was designed and built in New Zealand in the late 1950s.

The test results give an indication of the performance of beam-column joints and members with the above now out-of-date reinforcing details.

The test results reported are a summary of results reported in a number of publications written since 1994.     

Turkey's isolated stance: an ally no more,or just the usual turbulence?

This article explores the policy choices and political stances that lie behind Turkey's growing isolation both from its western allies and its regional neighbours. It details Ankara's approach to a range of current issues in its region—particularly relating to Syria but also Iraq, Libya, Iran, Russia and Israel—and seeks to trace these approaches back to the world‐view of the country's ruling party and its leading figures, most notably President Erdogan and Prime Minister Davutoglu. It also assesses Turkey's reactions to the complex regional circumstances that have confronted Turkey in recent years. It considers the content and impact of some of the rhetoric emanating from Ankara, especially where it is directed towards the West. The article asks whether and why Turkish foreign policy has acquired an anti‐western tone, and also looks at the extent to which its dealings with its neighbours can be explained by sectarian considerations or by pro‐Muslim Brotherhood leanings. It then goes on to speculate about Turkey's future relationship with NATO and to a lesser degree the EU. It considers the prospects for an improvement in Ankara's relationship with its western allies, or whether Turkey–US relations in particular are now likely to be characterized by ‘strategic drift’ and a more transactional and contingent approach to alliance relationships.     

ESTIMATION OF THE AGE OF A PRE‐INDUSTRIAL IRON SITE IN KOREA*

A pre‐industrial iron‐smelting site in Korea, whose period of active use is placed on typological grounds between the eighth and 18th centuries ad , has been dated using accelerator mass spectrometry and thermoluminescence. The ages of two charcoal samples were 77 ± 25 and 81 ± 25 years bp , with the calibrated date for both ranging from ad 1700 to ad 1955, while a clay fragment dated to ad 1650 ± 50. The results from typology and radiocarbon seem insignificant due to the considerable uncertainties involved, but in combination with the thermoluminescence result they place the most probable date of the site at around ad 1700.     

"韩流"对韩国旅游形象的影响

本文在广泛调查的基础上,运用多元统计技术分析了"韩流"对韩国旅游形象的影响程度,并探讨了访问意向与实际到访、游后评价以及旅游形象之间的关系等重要问题.